Lawrence B. Rees

Analysis of lichen thin sections by PIXE and STIM using a proton microprobe

Abstract In order to better understand the distribution pattern of mineral elements in lichen tissues, thin sections (15 μm) of the foliose, vagrant soil lichen Xanthoparmelia chlorochroa were examined using proton microprobe Particle induced X-ray emission (PIXE). This technique was used to make two-dimensional scans, with 5 μm resolution, across tissue cross sections of the test species. Element maps for Si, P, S, Cl, K, Ca, Ti, Mn, Fe, Cu, Zn, and As have been prepared. Several elements are strongly localized in the element maps. PIXE data are complimented with STIM, light micrographs, and SEM images. Preliminary data suggest that nuclear microprobe techniques may be useful in elucidating element absorption and transport mechanisms in lichens.

Characterization of mycobiont adaptations in the foliose lichen Xanthoparmelia chlorochroa (Parmeliaceae).

A cross section of the vagrant soil lichen Xanthoparmelia chlorochroa was analyzed using proton microprobe PIXE. Data were used to generate quantitative, two-dimensional element distribution maps for Al, Si, P, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, As, and Sr. Element maps show differential element partitioning between the stratified layers of the thallus. These data document transfer of inorganic nutrients across the thallus to the algal layer. Inorganic particle entrapment was also evident in the element maps. Dense accumulations of calcium oxalate at the junction of the medulla and the algal layer on the order of 10% by dry mass were discovered. Scanning electron microscopy and thermogravimetric analyses were used to characterize the calcium oxalate region. These data provide evidence for possible functional roles of the calcium oxalate layer, including regulation of water and light. Data also provide support for a mutualistic interpretation of the lichen association.

The Contribution of Sulfate and Nitrate to Atmospheric Fine Particles During Winter Inversion Fogs in Cache Valley, Utah

Abstract Air pollutants were collected in Logan, Cache County, UT, in February 1993 during two periods of atmospheric inversion accompanied by fog. The following atmospheric species were determined: (1) gaseous SO2, NO2 (semi-quantitatively),HNO3, NH3, and HF; (2) fine particulate SO4 =, NO3 -, NH4 +, F–, H+, C, Si, S, K, Ca, Ti, Mn, Fe, Ni, Cu, Zn, Pb, Se, Br, and Sr, and; (3) fine particulate mass, which was calculated. The major components of fine particulate matter were carbonaceous material, ammonium nitrate, and ammonium sulfate, while the soil component was small. Calculated, fine particulate mass averaged 80 μg/m3 and reached concentrations as high as 120 μg/m3. SO2/Sox and NO2/NOy mole ratios generally varied between 0.2 and 0.1 during inversions. These ratios also showed moderate but consistent diurnal patterns. The emission inventory for Cache County indicates sources of SO2 and NOx but not significant amounts of primary sulfate and nitrate. The observations reported here indicate there is sign...

PIXE ELEMENTAL ANALYSIS OF SOUTH AMERICAN MUMMY HAIR

Abstract Hair samples were obtained from ten mummies of the archaic and formative cultures of the north coast of Chile. Each sample was divided into two portions. One portion was washed in acetone and then water and the second portion remained unwashed. All samples were then prepared by an acid digestion procedure and analyzed by PIXE. The washed and unwashed samples were compared to determine what elements were present in the material on the hair surface. Concentrations of the elements Ca, Ti, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Sr, and Pb are reported. Comparison was made to previously published elemental analyses of mummy hair and modern hair. One sample, which had a reddish hue, was found to contain unusually large quantities of Fe and As. Since the unwashed sample had much higher concentrations of these elements than the washed sample, it is believed that the reddish color originated in a mineral dye applied to the hair.

Elemental analysis of lichens from the intermountain western USA using PIXE

Abstract Thirty-six lichen samples that were collected from five wilderness areas and a national monument in the intermountain western United States have been analyzed by PIXE for the determination of 21 elements: P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Br, Rb, Sr, Ba, and Pb. Samples were powdered and spiked with Y as an internal standard. The powder was analyzed directly as a sample of moderate thickness. Elemental concentration means and ranges were generally consistent with concentration ranges from other studies of unimpacted lichens. Some samples, however, had high concentrations of S, Cu, As, and a few other elements. There are interpretations of the data that imply some wilderness areas are being impacted to some degree by industrial-plant atmospheric emissions.

Regional Source Profiles of Sources of SOx at the Grand Canyon During Project Mohave

Total fluoride (gas plus fine particle), spherical aluminosilicate particles, particulate selenium, arsenic, lead, bromine, and absorption of light by fine particles have been used to characterize chemical profiles for sources of sulfur oxides impacting the Grand Canyon National Park Class I Visibility Region. During the Project MOHAVE (Measurement of Haze and Visual Effects) winter and summer intensive studies in 1992, these various species were determined at seven sampling sites in and around the Grand Canyon. Extensive upper air and surface-based meteorological measurements were examined to determine probable geographical origins of the air mass present during a given sampling period for each sampling site. Samples corresponding to air masses dominated by transport from a single major source region were used to determine a source profile for each region. Source regions which have been characterized by this analysis include the San Joaquin Valley area, the southern California coastal urban area, the Baja, California-Imperial Valley area, the Arizona and Mexico area (including major smelters) south of the Grand Canyon, the area southeast of the Grand Canyon, the Colorado Plateau area, the Wasatch Front in Utah, and the area in Nevada to the west and northwest of the Grand Canyon. Source profiles giving the ratio of each endemic marker to SO x for each identified regional source in these areas have been determined. The source profiles for the various regional sources are all statistically different and distinguishable from those for other geographically adjoining sources.

Determination of aluminum oxide stopping cross sections for protons and deuterons by backscattering from thin targets

Abstract Self-supporting foils of aluminum oxide in the thickness range 100 to 300 nm were prepared by anodic oxidation of aluminum foil and subsequent dissolution of the unreacted aluminum. The foil thicknesses were measured by scanning electron microscopy. Using these foils, stopping cross sections of aluminum oxide for protons and deuterons were measured for particles in the energy range 0.90 to 2.50 MeV. These measured stopping cross sections are compared to other literature results and to the theoretical values as predicted by Braggs Rule.

Analysis of Rocky Mountain lichens using PIXE: Characteristics of iron and titanium

Lichens have been shown to be effective biomonitors of air quality. They are currently being used to characterize background element levels and to identify air pollution effects on federally administered lands in the Rocky Mountain region of the western United States. PIXE analysis for twenty elements has been performed on over two hundred lichen specimens collected from various national forests, national monuments, and national parks in the region. This paper reports on patterns of iron and titanium accumulation in lichen tissues. Data show a strong relationship between concentrations of iron and titanium. The Fe/Ti ratios agree well with values reported in similar lichen studies; however, our values for both iron and titanium concentrations are ten times greater than other reports. A distribution function for the log of iron concentrations is distinctly bimodal. The lower concentration mode contains fruticose lichens from bark substrates and the higher concentration mode contains foliose lichens from rock substrates. High iron concentrations in fruticose lichens along the Wasatch Front suggest air pollution impact from a local steel plant.Lichens have been shown to be effective biomonitors of air quality. They are currently being used to characterize background element levels and to identify air pollution effects on federally administered lands in the Rocky Mountain region of the western United States. PIXE analysis for twenty elements has been performed on over two hundred lichen specimens collected from various national forests, national monuments, and national parks in the region. This paper reports on patterns of iron and titanium accumulation in lichen tissues. Data show a strong relationship between concentrations of iron and titanium. The Fe/Ti ratios agree well with values reported in similar lichen studies; however, our values for both iron and titanium concentrations are ten times greater than other reports. A distribution function for the log of iron concentrations is distinctly bimodal. The lower concentration mode contains fruticose lichens from bark substrates and the higher concentration mode contains foliose lichens from ro...

A Monte Carlo calculation of secondary electron bremsstrahlung in PIXE

Abstract One of the primary components of the background in PIXE spectra is secondary electron bremsstrahlung (SEB). However, in order to evaluate the integral usually used to calculate SEB cross sections, certain simplifications must be made, such as assuming an infinite target thickness. In order to more realistically model the physical processes involved in SEB, a Monte Carlo approach is useful. SEB cross sections are calculated by Monte Carlo techniques and the results are compared with the work of Ishii, Morita, and Tarawa [Phys. Rev. A13 (1976) 131; Int. J. PIXE l (1990) 1]. To demonstrate the flexibility of the Monte Carlo method, effects due to the target thickness and the proton-electron cross section are examined.

A study of the reaction (π+, π+ p) in 12C and 6Li

Abstract We have measured the angular and momentum distributions of the scattered pions from the reaction 12C(π+, π+p)11B and 6Li(π+, π+ p)5He in a coincidence experiment. We compare our results with the plane and distorted wave impulse approximations.